1. Field of the Invention
The present invention relates to a purified solution containing iron chloride and manganese chloride and to a method for producing the solution. The purified solution is oxidized by roasting in order to produce a mixed oxide powder containing iron and manganese, thus being useful as a raw material for manufacturing a high-quality soft ferrite of excellent magnetic properties.
2. Prior Art
To manufacture soft ferrite, an iron oxide powder, a manganese oxide powder and other metal oxide powders, for example, zinc oxide powder are prepared. Also, a compounded powder with a compounding ratio of Fe.sub.2 O.sub.3 :MnO:ZnO, for example, 70.6:14.2:15.2 in weight is produced. The compounded powder is then sintered at about 1,300.degree. C. and soft ferrite is manufactured. To manufacture ordinary soft ferrite of ordinary magnetic properties, an iron oxide powder of ordinary grade is used.
In prior art methods, iron oxide powder of ordinary grade is produced by roasting a waste hydrochloric pickling solution of steel. In the roasting furnace at about 700.degree. C., iron chloride in the solution is oxidized according to the following formula (1). EQU 2FeCl.sub.2 +H.sub.2 O+O.sub.2 .fwdarw.Fe.sub.2 O.sub.3 +2HCl(1)
In the above methods, a waste hydrochloric pickling solution is sprayed into the roasting furnace, and powdered Fe.sub.2 O.sub.3 is obtained from the roasting furnace. Gaseous HCl in the discharged gas is changed to aqueous hydrochloric acid by any of several known methods. In general, this method is simple and the iron oxide powder produced is low in cost. Accordingly, the iron oxide powder thus obtained is widely used for manufacturing ordinary soft ferrite with ordinary magnetic properties.
However, the iron oxide powder produced by this process is not used for high-quality soft ferrite where more superior magnetic properties are required. In this particular method as explained, all impurities contained in the steel are dissolved in the waste hydrochloric pickling solution, and therefore are also included in the iron oxide powder. These impurities in the iron oxide powder impair the magnetic properties of the soft ferrite. In manufacturing the high-quality soft ferrite, expensive oxide powders of high purity, i.e. a high purity iron oxide and a high purity manganese oxide, are exclusively used. Table 1 shows an example of the impurity content of iron oxide powder and manganese oxide powder for soft ferrite, as well as the impurity content of other materials which can be used as raw materials for both oxides. In Table 1, high-purity iron oxides A or B, and high purity manganese oxide are used for high-quality soft ferrite, and ordinary iron oxide is used for ordinary soft ferrite.
In another prior art method, high-purity iron oxides A or B are produced by a crystal refining method. In the crystal refining method the crystals of iron sulphate or iron chloride are crystallized from the aqueous solution thereof, and these crystals are oxidized by roasting to obtain an iron oxide. In this method, however, the impurities are not reduced sufficiently by a single crystallization, because part of the impurities are mixed in the crystals. Thus, the obtained crystals are dissolved again in water, etc., and the crystallization treatments are repeated, thereby reducing the impurity content. According to this method, an iron oxide powder of high purity, such as the high-purity iron oxides A or B in Table 1, can be obtained. However, the crystal refining method is complicated and the production cost of the iron oxide powder is high because of the repeated crystallizations.
Also in case of manganese oxide, impurities can be reduced by electrolysis or by the crystal refining method, but the process is complicated and the cost is high, as in the case of the high purity iron oxides.
Thus, general knowledge about the kind of impurities, as well as the permissible content level of the impure elements in the powdered oxide, which impair the magnetic properties of a high quality soft ferrite, has been insufficient. Another method to improve the powdered oxide of ordinary grades to a level sufficient for high-quality soft ferrite has not been found, the oxide powders produced by the crystal refining method, where impurities are significantly decreased for the formation of high quality soft ferrite, are very expensive.